The present invention generally relates to detecting devices and more particularly, to a pyroelecric type detecting device for detecting infrared rays or the like through their convergence by a converging mirror.
Generally, infrared sensors for detecting infrared rays are divided into a quantum type utilizing photoelectric effect of semiconductors and a thermal type utilizing thermoelectric effect or pyroelectric effect. The quantum type infrared sensors are quite highly sensitive. However, since response wavelength range of the quantum type infrared sensors is narrow and the quantum type infrared sensors are required to be cooled for detecting infrared rays, the quantum type infrared sensors are not widely used. On the other hand, detection sensitivity of the thermal type infrared sensors is low. However, the thermal type infrared sensors have such a feature as functioning at room temperature without dependence upon wavelength. Therefore, recently, the thermal type infrared sensors, especially the pyroelectric type infrared sensors are widely used in various fields.
The pyroelectric type infrared sensors are a kind of temperature sensors for detecting temperatures through utiliziation of pyroelectric effect that when temperature change is caused in pyroelectric crystals, electric charge is produced on the surfaces of the pyroelectric crystals upon spontaneous polarization. The pyroelectric type infrared sensors are used for detecting human bodies, flames and temperatures. As will be seen from the above described operational principle that temperature change is detected by electric charge produced on the surfaces of the pyroelectric crystals, the pyroelectric type infrared sensors have such drawbacks as high impendance and susceptibilty to external noises. Thus, in a pyroelecric type detecting device employing the pyroelectric type infrared sensor, it has been so arranged that a conveying mirror is provided in the vicinity of a mounting portion of the pyroelectric type infrared sensor so as to converge upon the pyroelectric type infrared sensor, infrared rays emitted by a source generating the infrared rays such that a signal-to-noise (S/N) ratio is increased.
In the known pyroelectric type detecting device referred to above, the pyroelectric type infrared sensor is secured to a frame or the like having the converging mirror attached thereto and the frame is angularly adjustably mounted such that a direction of incidence of infrared rays can be set arbitrarily. However, if the frame is angularly adjustably mounted such that infrared rays are set at a direction of incidence as described above, such problems arise due to relatively large size of the frame having the converging mirror attached thereto that a range of directions of incidence of infrared rays is restricted and a site for mounting the pyroelectric type detecting device is limited.
In order to eliminate such problems of the known pyroelectric type detecting device, it will be considered that the pyroelectric type infrared sensor smaller in size than the frame for the converging mirror is arranged to be moved relative to the frame so as to adjust the direction of incidence of infrared rays. However, in this case, a lead wire (usually, a shielding wire) extending from the pyroelectric type infrared sensor to an amplifier for amplifying an output of the pyroelectric type infrared sensor is displaced through positional adjustment of the pyroelectric type infrared sensor, thereby resulting in change of stray capacitance of the lead wire. The pyroelectric type infrared sensor has a high impedance as described above. Thus, when the stray capacitance of the lead wire changes, noise components inputted to the pyroelectric type infrared sensor vary and thus, such an inconvenience is incurred that an S/N ratio of an input signal to the amplifier changes according to adjusted positions of the pyroelectric type infrared sensor.